The present invention relates to a method for the manufacture of a coated plasterboard as well as the product in which a mixture is produced which consists of gypsum, water and fibers, and this mixture is formed into a sheet and then applied to at least one of the major areas of the plasterboard and the entity is then moved through grooved rollers or bandconveyors.
In a method of the above-mentioned type, (Cf German Pat. No. 1,033,123), a glass fiber fleece, while being applied to the plasterboard, is impregnated with pure gypsum, and the mixture which which the plasterboard is covered is in an expanded foamy condition. This method is relatively difficult to carry out since two different gypsum mixtures of various thicknesses must be securely combined with each other while both are in a wet state, and which will rarely have the desired uniformity. In addition, the pure gypsum will form residues on the metal of the grooved rollers or band-conveyors, which will clog the conveyors.
In addition to the above-mentioned plasterboard covered by a glassfiber fleece, there are also products known as plaster pasteboard sheets, identified by the German Industry Norm (DIN) as 18,180. Plaster pasteboard sheets are manufactured on belt conveyors in a manner so that a watery solution of burned gypsum having certain additives, is continuously formed and hardened between pasteboard sheets and the resulting product is then cut to the desired size. On the band-conveyors for the manufacture of plaster pasteboard sheets, the bottom pasteboard sheet has two edges which overfold and the cavity formed by the bottom sheet and its edges is filled with a plaster mixture and is moved to a forming table. At the same time, an upper pasteboard sheet, which enters on an upper grooved roller, covers the cavity to make a sandwich. The hardening occurs on a setting board, and after cutting to the desired length, the so-formed plaster pasteboard sheet is then dried in a roll-conveyer dryer.
Defects develop when the plaster pasteboard sheets are used as cover plates, according to the system of blind sheathing as disclosed in the German Auslegeschrift No. 1,287,992 and the German Offenlegung No. 1,434,513. Adhesion defects result, especially on the exposed side or surface of the plaster pasteboard, and in unfavorable or construction-site conditions, complete removal of the pasteboard layer of the plaster pasteboad sheet becomes necessary before the finishing material is applied. Furthermore, mold will appear on the exposed side of the plaster pasteboard sheet as a result of the continued effects of humidity, and the mold must be removed.